As depicted in FIG. 1, an Ethernet link 11 is a connection between two adjacent Ethernet devices 10A or 10B, while an Ethernet path 13, as depicted in FIG. 2, is a connection between two Ethernet devices 10A or 10B via a network 12 composed of multiples links, which may or may not be using Ethernet. The Ethernet device 10A, 10B, may be a network element device, such as a router, a switch, etc. or could be a simpler device, such as a personal computer (PC) or other terminal device. In case of a network element device, the Ethernet traffic may originate from or be destined for the device itself or from other devices behind it. The Ethernet link 11 and the Ethernet path 13 can be called an Ethernet circuit. The testing of an Ethernet circuit includes transmitting test traffic from one location toward an Ethernet device 10A or 10B. The test location may be anywhere on the Ethernet circuit. Test traffic reception processing, which may include validation, counting, bandwidth determination, etc., is not necessary, albeit useful, for the purpose of this invention.
The test traffic uses specified attributes (e.g., Ethernet ethertype, data payload, priority parameters, IP or MAC addresses, packet size, etc.) and specified transmission characteristics (such as bandwidth, burst size, test duration, etc.). The goal of the testing is to verify the ability of the Ethernet link 11 or path 13 to successfully convey Ethernet frames from one device 10A or 10B to another Ethernet device 10B or 10A under the specified conditions (packet attributes and transmissions characteristics). The traffic attributes or transmission characteristics used for a given test session may be set to any desired value as necessary but the operation of this invention does not depend on any setting. The Ethernet link 11 or path 13 is said to be in-use or in-service when traffic other than the test traffic is present on the said Ethernet link 11 or path 13 at the location where test traffic is transmitted.